Welding method and thermostat produced

ABSTRACT

A method of welding electrical contacts onto conductive bodies including engaging a surface of the contact with the conductive body and passing a welding current through a pair of spaced surface areas of the contact to provide weld action and wherein a rib portion between the pair of spaced areas retains unoxidized metal thereon to improve electrical contact properties of any article made and utilizing the contact and particularly the ribbed area thereof for make and break engagement with other members of an electric circuit. 
     A new control article is also provided wherein a contact therein has a raised center rib thereon for contacting an associated means for make and break circuit action, which contact is made from silver or silver alloy and has uncontaminated silver on the surface of the rib or center area of the contact.

This is a division of application Ser. No. 419,774, filed Sept. 20,1982, now U.S. Pat. No. 4,489,228.

TECHNICAL FIELD

A welding method involving use of a bifurcated welding arbor inassociation with a relatively soft metal contact, such as a silvercontact, wherein the welding action usually causes a center ridge to beformed in the contact between the weld arms of the arbor. Also, a newwelding or securing technique is disclosed using an arbor for producinga ridge line or an uncontaminated center area in the end product.

BACKGROUND ART

In the formation of small electrical products, such as motor protectors,thermostats, and the like the industry has used silver contacts for manyyears to aid in obtaining good electrical properties in the products andto provide desirable, accurate control actions. These silver contactsbecome oxidized in use and they usually also have been microscopicallycorroded in the welding or riveting fabrication of the control. Suchcorrosion is objectionable.

Typical patent showing thermostats, such as the types to which thepresent invention relates are U.S. Pat. Nos. 3,721,934; 3,141,322 and2,586,309. In such articles the contacts are secured in place byconventional weld techniques.

DISCLOSURE OF INVENTION

The general object of the present invention is to provide a new andimproved welding method wherein the surface of the contact that providesmake and break contact with an associated member has not beenimpregnated, contaminated or appreciably oxidized by the weldingelectrode used for attaching the contact to a carrier member.

Another object of the invention is to provide electrical contacts thathave ridges provided thereon to facilitate make and break electricalcontact with an associated electrical member and wherein the ridgeportion of the contact is uncontaminated and provides an effectiveelectrical contact medium with constant properties over a long servicelife.

Another object of the invention is to provide an uncontaminated centerstrip or area on the surface of a metal contact.

Yet a further object of the invention is to provide improved motorprotectors thermostats and like electrical control items havingeffective, efficient lives with substantial uniform electricalproperties.

These and other objects of the invention will become more apparent as adetailed description of the specification proceeds, are achieved: by amethod of attaching electrical contacts onto a conductive body by use ofmetal contacts having an uncontaminated surface thereon including thesteps of supporting spaced surface areas of the uncontaminated surfaceof the contact, forcing the opposite surface of the contact intoengagement with the conductive body, and securing the contact to theconductive body but leaving a center area on the uncontaminated surfaceof the contact between the said spaced areas which center area hasunoxidized uncontaminated metal on its exposed conductive surface.

BRIEF DESCRIPTION OF DRAWINGS

Reference now is made to the accompanying drawings, wherein:

FIG. 1 is a vertical section through a thermostat having contactstherein positioned by the welding method of the invention;

FIG. 2 is an enlarged fragmentary plan view of a contact of thethermostat of FIG. 1;

FIG. 3 is a side elevation of the contact of FIG. 2;

FIG. 4 is a vertical section taken through the contact of FIG. 3 on line4--4 thereof;

FIG. 5 is a fragmentary vertical section showing the positioning of acontact on a weld arbor and positioned within a case preparatory toattachment thereto;

FIG. 6 is a vertical section showing the next tep of welding the contactto the interior surface of the metal case of FIG. 5;

FIG. 7 is a diagrammatic view of welding circuit and associated meansfor welding a contact to a member such as a bimetal strip;

FIG. 8 is a plan view of the lower weld arbor of FIG. 7;

FIG. 9 is a vertical section taken on line 9--9 of the weld arbor ofFIG. 8;

FIG. 10 is a plan view of a portion of a weld arbor of the invention;

FIG. 11 is a vertical section taken on line 11--11 of FIG. 10; and

FIG. 12 is a vertical section through a riveted contact assembly that isa modification of the invention.

When referring to corresponding members shown in the drawings andreferred to in the specification, corresponding numerals are used tofacilitate comparison therebetween.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference now is made to the details of the structure shown in theaccompanying drawings, and FIG. 1 shows a cross-section of a thermostat10 that includes a pair of contacts 12 and 14 positioned in opposedoperative relationship with each other and wherein at least one of thesecontacts and the thermostat article made therefrom responds to thefeatures of the present invention.

Specifically, in the thermostat 10, a bimetal strip 16 extends into thecase 18 of the thermostat and is sealed in the case 18 by conventionalsealing sleeve or means 20. At the free end of the bimetal strip 16,contact 12 is welded thereto while contact 14 is shown welded to thecase 18 on the interior surface thereof in opposed relationship to thecontact 12.

FIGS. 2 and 5 show how a contact, such as the contact 12 is secured inposition within the case and thus a weld arbor 22 is shown and itextends into the case 18 for securing a contact thereto. The end of thearbor shown is bifurcated and it includes a recess 26 on the surfaceshown uppermost in FIG. 2. Legs 24 and 25 of the arbor extend the heightof the arbor at this welding end of the member and the contact 12 isreceived in the recess 26 usually adjacent the inner end thereof. Therecess is shallower than the contact so that the contact will protrudeabove the arbor. This contact 12 is of the type used in many instancesin making thermostats, motor protectors and the like wherein the contactis formed from substantially pure unoxidized silver. A base surface ofthe contact is thus exposed for bearing on the interior surface of thecase.

FIG. 6 shows that a weld arbor 30 is in engagement with the outersurface of the case 18 and is directly opposed to the base surface ofthe contact 14 as positioned. Thus, the arbor 22 brings the base surfaceof the contact into engagement with the case and welding current is thencaused to flow between the arbor 22, the contact 14, the case wall 18and the arbor 30. Some slight weld pressure is exerted on the contact atthis time by the legs 24 and 25 of the arbor and the contact is weldedto the case.

FIG. 2 shows a fragmentary enlarged plan of part of the thermostat ofFIG. 1 and particularly of the contact 14. A feature of the inventionthat an upstanding rib 32 is formed on the contact by the weld actionprovided and the size or height of the rib is controlled by the weldingconditions and composition of the contact. This rib 32 normally extendsacross a diameter of the contact and it may decrease slightly in heightadjacent diametrically opposed ends thereof. However, such rib 32 hasbeen produced by the pressure and heat of weld action and by the legs 24and 25 of the arbor during welding. This metal forming the rib 32 hasnot been contacted at all during the welding and hence, the contact willretain a pure silver unoxidized, uncontaminated surface on the rib sincethe contacts are made from pure unoxidized silver or other pure metals,and only current carrying surfaces of the contact become oxidized duringthe welding.

When a contact of the invention is to be secured to any type ofconductive body, apparatus more or less as diagrammatically shown inFIG. 7, can be used for the welding action of the invention. In thisinstance, a bimetal strip i.e., conductive body 40 is shown and acontact 42, like the contact 12 is to be secured to one surface of thestrip 40. Thus, a base arbor 44 which may be of cylindrical shape andhave a bifurcated upper end 46 with legs 47 and 48 is provided. A toparbor 50 is positioned in opposed operative relationship with the arbor44 and one of these arbors is movably positioned so that the arbors canbe brought into operative engagement with the bimetal strip 40 andcontact 42 therehetween. Then when all members are brought into contact,power supply 52 is actuated for desired weld action. This weld actionprovides, again, as in the prior embodiment of the invention, a contactthat has a center rib thereon like the rib 32 and wherein such portionof the contact and its surface has not been contaminated by nor beeninvolved in the weld action. If necessary, some type of a supportsurface, rib, or recess could be provided on the base weld arbor 44 tohave it aid in centering a contact thereon and thus, the top surfacecould be like the recessed top surface of the arbor 22. A typicallyelongate arbor 22 is shown in FIG. 10 and these parallel spaced legportions of the arbor at its inner end thereof readily position acontact for the weld action of the invention.

FIG. 12 shows a further securing method for obtaining a contact with anuncontaminated metal surface. A rivet arbor 60, like the arbor 44, isused to support a pure metal or metal alloy contact 62. This contact hasa tang 63 extending therefrom through a hole in a bimetal strip 64 orother metal object to which the contact is to be secured. A spreadertool or punch 66 is forcibly brought into contact with the stem or tang63 to upset the metal and tightly secure the contact 62 to itsconductive carrier 64. The pure metal surface of the contact 62including a center area 68 thereof extending across the contact hencehas not been worked or contaminated in any manner by the rivet action,and microscopic contamination, as obtained in riveting and weldingactions is avoided. Such center area 68 is not supported during therivet action and hence a shallow raised rib may be produced at suchcenter area depending on the contact material used, the metal workingpressure etc.

From the foregoing it will be seen that a novel and improved weldingmethod and apparatus has been disclosed for small electrical articlesand especially where controlled resistance is desired in the articles.The contacts in the control articles in the invention have minimalresistance and will provide long service lives with no changes in theresistance or in functioning over some thousands of operative cycles.The thickness of the center ribs on the contact can be controlled by thelength of the weld current passed and by the welding pressures and bythe type of welder design. This improved securing method of theinvention can be used to position contacts or other members on any othertype of a conductive body and provide a center contact area withunoxidized metal thereon.

When two contacts are positioned in opposed relationship as shown inFIG. 1, the raised center ribs on these contacts can be positionedparallel to each other, usually to provide best contact therebetween.However, if desired, the center ribs could be positioned in 90° spacedrelationship to each other and still have good contact engagementbetween the center raised contact areas of the ribs, or only one contactmay have a rib, or uncontaminated surface area thereon. Thus, it isbelieved that the objects of the invention have been achieved and thatimproved, accurate electrical controls can be provided and whichcontrols would have a good operative service life.

While one complete embodiment of the invention has been disclosedherein, it will be appreciated that modification of this particularembodiment of the invention may be resorted to without departing fromthe scope of the invention.

What is claimed is:
 1. A thermostat, motor protector or the likeincluding:a case; a bimetal strip extending into said case as acantilever and having a hole formed in the cantilever part thereof; ametal contact member within said case on said strip for making andbreaking an electrical circuit; and said contact member having anuncontaminated center area extending across its contact surface, saidcontact member being made from pure unoxidized, uncontaminated metal,and said contact has a tang extending through said hole to secure saidcontact member to said strip.
 2. A thermostat, motor protector or thelike including:a case; a bimetal strip extending into said case as acantilever; cooperating contact members within said case for making andbreaking an electrical circuit, one of said contact members beingsecured to said bimetal strip; and at least one of said contact memberhaving a rib extending across its contact surface, said ribbed contactmember being made from pure unoxidized silver, and the surface of saidrib comprises pure unoxidized silver, where the ribbed contact member issecured in place in the unit by welding and no electrical contact ismade with the surface of the rib during the welding.